The present invention relates to a method for generating an image from an object which is scanned strip-wise, these strips being combined into an image.
Such methods are known especially for generating thermographic images and also for generating infra-red (IR) images. Using a suitable optical means, for instance a polygonal prism with pairwise dihedral surfaces, images of object strips are projected on a striplike set of detectors consisting of several individual detectors arranged normally to the direction of motion of the strips of the object image.
To the extent a method or apparatus for generating images of objects by means of non-visible beams is concerned, the detectors control in known manner correspondingly arrayed light-emitting-diodes (LEDs) of which the visible beams then are preferably combined by the same optical means into a visible image. However, the detector can also be used to generate a video image.
Such a method, especially a polygon suited to generate image lines, is known for instance from German Published Application No. 25 22 049.
The design and operation of such a "dihedral polygon" has already been comprehensively described especially in the German Published Application No. 25 22 049, already mentioned. It is an essential characteristic of such a polygon that for one revolution of this polygon, the image will be written only once. It does not matter in this respect in what sequence the strips of the groups of lines of the image are being written, that is, whether in a constant manner as in FIG. 7, or alternatingly, as in FIGS. 8 and 9 of German Published Application No. 25 22 049, which are shown schematically, and explained in relation thereto.
The fact that the image is written only once per polygon revolution, however, results in a definite image line always being projected on the same detector. This presents the significant drawback that if this detector should fail, the information of this line will be lost, nor will it be retrieved after several further revolutions of the polygon, since it is always the same line which falls on the inoperative detector. In such a case there obtains a so-called "line wild-shot". If such an imaging instrument is used for instance as a target lock-on, point targets may well fall into the "dead" or dark line, get lost and be detected again only after the entire instrument has been moved.